Well blow me if the British Council haven't mentioned the Cornish language on their website. A reasonably honest and positive take on things as well. See below:
When did the language die out? It really depends on your definition of 'died out'. The story goes that the last person who spoke Cornish (and no English) was a woman called Dolly Pentreath. She died in 1777 and some people say that the language died with her. But of course, there were still people who spoke Cornish as a native language, even if they also knew English. And their children learned some Cornish from them even if they spoke English most of the time. The number of speakers got smaller and smaller and they knew less and less of the language, but Cornish didn't disappear. There are stories of fisherman still using Cornish numbers to count fish in the 1940s and 50s. So some people argue that the language never died out completely, but survived until the Cornish revival started at the beginning of the twentieth century.
On the Subject of Cornish UNESCO has this to say in a recent press release:
Certain languages are even showing signs of a revival, like Cornish, a Celtic language spoken in Cornwall, southern England, and Sishee in New Caledonia.
More from UNESCO on languages here: Intangible Cultural Heritage and Endangered languages. Is the UN distinction of Cornish as an extinct language justified then? Christopher Moseley, an Australian linguist and editor-in-chief of the atlas is reported by the BBC, who otherwise seem to gloat over the 'extinct' classification of Cornish, to have said:
"I have always been optimistic about Cornish and Manx.
"There is a groundswell of interest in them, although the number of speakers is small.
"Perhaps in the next edition we shall have a 'being revived' category.
"[Cornish] is among a group of languages that turned out not to be extinct but merely sleeping."